64 CTENOPHOKA 



1. In general appearance a specimen resembles a hy- 

 drozoan medusa, with its aboral surface elongated until, as a 

 whole, it approaches the shape of a fowl's egg. 



2. The broader or oral end bears two small lip-like lobes, 

 between which is the slit-like mouth. We may consider the 

 elongation of the mouth to be in the anteroposterior plane. 

 Bilateral symmetry is thus evident. 



3. At the aboral pole is the "sensory body" 



4. Leading away from this and extending as meridional 

 lines toward the oral pole are eight ctenophoral rows of 

 swimming plates. Examine the plates with a hand lens and 

 determine their structure and function. Determine the po- 

 sitions of the rows with respect to the anteroposterior plane. 



5. By the sides of the stomodaeum are a pair of yellow- 

 ish or orange tentacles that may be retracted wholly into the 

 tentacle sheath or extended through pores near the aboral 

 pole. When extended the tentacles are seen to be branched. 

 They are very sensitive and contractile. 



Digestive System. — With a pipette inject a solution of 

 carmin into the mouth opening. 



1. You can then more plainly see the long ribbon-like 

 stomodaeum which extends two thirds of the distance to the 

 sensory body, where it joins the infundibulum. 



2. From the stomodaeum are given off the canals, which 

 in a successful injection will be seen to be as follows: 



(a) The axial funnel tube extending to the sensory body. 



(b) Two par agastric canals, one on each side, passing 

 down along the stomodaeum. 



(c) Two tentacular canals, one on each side, passing to 

 the tentacular structures. 



(d) Two perradial canals, one on each side, each of which 

 bifurcates to form the interradial canals (four in all), each 

 of which again bifurcates to form the adradial canals (eight 

 in all), which are continued orally and aborally just beneath 

 the swimming plates as the meridional canals. These canals 

 end blindly without intercommunication. 



